The aim of this project is to elucidate the biochemical pathways through which gonadotropic hormones control the metabolism and steroidogenic responses of the interstitial cells of the testis. This includes the characterization of gonadotropin receptors for Lh and FSH in the testis, and the analysis of the coupling mechanisms between receptor occupancy and androgen synthesis. The two major questions examined are: (1) the relationship of receptor occupancy to cyclic AMP and protein kinase during initiation of the steroidogenic and trophic actions of gonadotropin, and (2) the secondary sequence of events which leads to stimulation of the steroid biosynthesis pathway of the interstitial cell. This program has relevance to reproductive endocrinology, and is also aimed at a more general understanding of the mechanism of action of peptide hormones upon target cells. BIBLIOGRAPHIC REFERENCES: Podesta, E., Dufau, M.L. and Catt, K.J.: Characterization of two forms of cyclic 3',5'-adenosine monophosphate-dependent protein kinase in rat testicular interstitial cells. Mol. Cell. Endocinol. 5:109-122, 1976. Podesta, E., Dufau, M.L. and Catt, K.J.: Adenosine 3',5'-monophosphate-dependent protein kinase of Leydig cells: in vitro activation and relationship to gonadotropin action upon cyclic AMP and steroidogenesis. FEBS Letters 70, 212-216, 1976.